1. Technical Field
The present invention relates to the deposition of metal alloys and more particularly to Nixe2x80x94Fexe2x80x94Co alloys.
2. Background of Related Art
Chromium plating offers unique deposit properties, including brightness, discoloration, stability at atmospheric conditions and long preservation of the luster. But the uniformity of the deposit is poor, the required current density is high, current efficiency is low, and the cost of energy is great. At the same time, chromium ions are poisonous. Chromium salts which escape in the form of a mist, or through the drainage of wastewater, present an environmental hazard, adversely affecting both the air and water resources, and pose a risk to human health.
It would be desirable to provide the beautiful color and luster, good corrosion resistance and excellent wear resistance of chromium coatings without the aforementioned shortcomings. Many substitute for chromium deposits have been investigated and developed, of which Snxe2x80x94Co alloy is most promising. See, U.S. Pat. Nos. 3,966,564 and 3,951,760, the disclosures of which are incorporated herein by reference.
Compared with chromium plating deposits, Snxe2x80x94Co alloy deposits have the following advantage:
(1) Snxe2x80x94Co alloy deposits have the same luster and color as chromium deposits and can be used as decorative deposits.
(2) Corrosion resistance of Snxe2x80x94Co alloy deposits is superior to that of chromium deposits and be used as advanced protection deposits.
(3) Snxe2x80x94Co alloy deposits have good adhesion, excellent toughness, low internal stress, no porosity and no cracks.
(4) Throwing and covering power are very good.
(5) Current efficiency of Snxe2x80x94Co alloy plating is one to four times higher than that of chromium plating.
(6) Because Snxe2x80x94Co alloy plating is not poisonous, draining wastewater and mist can be easily handled.
But the hardness of Snxe2x80x94Co alloy deposits is about Hv 500-600, and wear resistance is only one half that of chromium plating deposits.
In order to overcome the disadvantages of Snxe2x80x94Co alloy deposits, some alloy deposits described have been developed as a new substitute for chromium deposits. For example, U.S. Pat. No. 4,529,668 discloses the electrodeposition of Co-B alloy. U.S. Pat. No. 5,614,003 discloses electroless deposition of Nixe2x80x94Moxe2x80x94P, Nixe2x80x94Cuxe2x80x94P, Nixe2x80x94Snxe2x80x94P, Coxe2x80x94Wxe2x80x94P and Nixe2x80x94Wxe2x80x94P alloys. These coatings have high hardness good wear resistance, and also have good corrosion resistance. But common problems in these process are that deposition rate is low, current efficiency is low and the cost of energy is great. For example, the electrodeposition rate of Coxe2x80x94Wxe2x80x94B alloy (U.S. Pat. No. 4,529,608), is only 1.6-50 xcexcm in six hours.
U.S. Pat. No. 4,833,041 discloses depositing on a substrate a quaternary alloy of nickel, cobalt, thallium and boron. The deposition is preferably electroless, but may be electrolytic, using a nickel anode and the substrate as the cathode, and using a fifty amps per square foot DC current. The electroless coatings comprise hard, amorphous, nodular deposits of metal alloy in somewhat softer metal or alloy matrix. The mass composition of the coasting has a ratio of nickel to cobalt of from about 45:1 to 4:1, the preferred compositions having a ratio of at least 5:1. The coating is heterogeneous in thickness cross-section, having higher cobalt concentrations at the interface of the coating and substrate. With heat treatment at 375 degree F., the nodules showed crystalline domains of metal borides dispersed in the metal alloy matrix. The heat-treated coating is reported to have knoop hardness values between 1230-1300. But thallium ions make the deposited surface passive and decrease the deposition rate too much. The techniques described in the ""041 patent produce a coating with a rough surface.
U.S. Pat. Nos. 5,213,907, 5,314,608 and 5,431,804 disclose a dense, smooth, ductile, hard, highly reflective, corrosion resistance, temperature resistance and wear resistant cocrystalline alloy of nickel cobalt and boron. The alloy is epitaxially electrodeposited on an activated substrate using a pulsed square wave current. The epitaxial deposition occurs in an electrolytic bath containing nickel ions, cobalt ions, complexing agents, wetting agent, stress relief agent and an amino borage compound at a moderately low pH level and moderate temperature. An insoluble, solid catalyst, preferably palladium, causes the alloy to diffuse into the surface of the substrate and become bonded to it by a polar-covalent bond. But the patent doesn""t disclose a complexing agent, wetting agent and stress relief agent. In order to get a good property of the coating, the current parameters, plating conditions and solution concentrations should remain constant. The chemical composition of the plating solution must be continuously analyzed and automatically. All of these conditions are very difficult to achieve in large scale production.
In order to overcome these disadvantages of prior known plating compositions and methods the present invention has been developed.
A novel alloy composition is provided herein. The alloy comprises from about 65 percent to about 75 percent by weight of nickel, from about 0 percent to about 20 percent by weight of iron, from about 15 percent to about 25 percent by weight of cobalt and from about 0.5 percent to about 1.5% of a hardening agent as defined herein.
The alloy is prepared by electrodeposition from a plating solution containing in solution based on the total metal content by weight of the solution from about 0 percent to about 25 percent iron, from about 10 percent to about 30 percent cobalt, from about 50 percent to about 80 percent nickel, from about 8 percent to about 20 percent of a reducing agent, from about 5 percent to about 15 percent of a completing agent and from about 3 percent to about 8 percent of a reducing agent.
The alloy can be deposited by (a) providing a substrate; (b) preparing the plating solution described above; (c) contacting the substrate with the plating d) providing an anode; and (e) applying an electric current to the anode and to the substrate for depositing a coating of the Nixe2x80x94Fexe2x80x94Co alloy onto a surface of said substrate.